One problem usually and often encountered in the production of concrete blocks is that mixes with a preponderance of coarse aggregates do not pack well in the high-production block molding machines, such as high speed vibration molding machines, used to produce such blocks. The improper packing of the coarse aggregate leads to the formation of improperly molded blocks that are structurally unsound or weak. The problem is especially pronounced when the conventional concrete block mix contains the highly desirable lightweight aggregates, such as cinders, pumice and those that are produced by burning of clay, shale or the like. In such cases the block mixes are very hard to pack properly and do not have the usual cohesiveness that is characteristic of traditional high density sand and gravel aggregate mixes with a traditional, conventional gradation in sizes and relative proportions of coarse and fine constituents.
Moreover, certain concrete blocks are known as "problem" blocks because their size, shape and/or face shell characteristics render them difficult to mold and handle even when generally acceptable well-graded aggregate is employed. As examples of such problem blocks there can be mentioned, for example, the two-core 12 inch block which has long and wide unsupported face shells, the 6 inch concrete block having thin face shells, as well as bond-beam blocks that have unique shapes and 2 inch patio blocks, which being solid, require a large amount of block mix material uniformly packed over a large top-of-mold area. Since patio blocks are molded on edge in the vertical plane, the top of the block in the mold is actually one of the edges, which sags, and thus often has an undesirable concave edge as molded. In addition, paving blocks are an especially difficult problem block to mold because being only about 35/8 inches high with a relatively large top area of 18.times.24 inches, this large area of the paving block contacting the molding machine's pressure head tends to stick to the pressure head plate because of suction. On unmolding of the paving blocks from the mold many of these tops are actually "torn" from the remainder of the block, causing defective blocks.
Furthermore, in producing any concrete blocks whether problem blocks or not, when there is a deficiency or diminished gradation of fine aggregate in the concrete block mix, a particularly acute problem of cracking and splitting occurs when blocks employing such mix (that is deficient in fines) is manufactured in high speed vibration block molding machines. Such cracking and splitting generally occurs most frequently upon ejection of the molded block from the machine's mold box. Moreover, it has been practically impossible to mold any type of acceptable concrete blocks when a block mix is not merely deficient in fines but where such fines are entirely absent.
In the prior art production of problem blocks, it has been accepted for many years at block manufacturing plants that a substantial percentage of cracked and defective blocks will usually result during each molding and curing cycle. Such useless blocks are known as "culls". They are crushed, and the resulting fragments and particles are recycled as coarse aggregate. It has been accepted practice to tolerate and be content with an overall "cull" production rate of generally about 5% or more, and in some cases up to about 10% or even up to 20% of the overall production runs of the various problem blocks or up to 20% of the run of non-problem blocks when using "problem" aggregates. Moreover, such problem aggregate cracking in about 90% of the blocks produced has been experienced, and the industry has had to accept the use of these cracked but still somewhat serviceable blocks, because such high percentages of cracking was considered inevitable by those in the industry. Such "culls" represent a substantial loss in productivity, a substantial economic drag on a block-making plant, and lead to increased costs. It would therefore, be highly desirable to provide an additive for a block mix which would dramatically reduce or even eliminate culls when producing the particular shapes and types of blocks which have previously been considered to be problem blocks.
Even in the production of ordinary non-problem blocks, there is a significant incidence of "culls", up to about 5% of the production runs. It would be highly desirable to provide an additive for a block mix which would substantially avoid or eliminate culls in the production of ordinary, run-of-the-mill, non-problem blocks of all types.
It is highly desirable for numerous reasons known in the art to want to produce or manufacture lightweight concrete blocks. In view of the aforementioned difficulties of molding acceptable concrete block using lightweight coarse aggregate or coarse aggregate deficient in fines, concrete block manufacturers who are producing such lightweight concrete blocks have found it necessary to add sand or stone dust, for example, to attempt to provide the necessary cohesive effect of fine aggregate in order that the block mix may be properly packed and acceptable blocks produced. However, the addition of such fine materials is highly disadvantageous in certain cases in that it undesirably increases the weight of the resulting concrete blocks thereby offsetting the advantages hoped to be gained by the use of the lightweight coarse aggregate. Moreover the addition of sand or stone dust does not satisfactorily cure the mold packing problem. It would, therefore, be highly desirable to provide an additive which enables block manufacturers to produce acceptable concrete blocks from lightweight coarse aggregate deficieht in fines and more particularly, lightweight coarse aggregate in which fines are totally absent and to do so without any substantial increase in the weight of the resulting concrete blocks.